Monopole towers are used to support antenna arrays for wireless telecommunication systems. Monopole towers typically comprise a monopole, which is a hollow tubular structures, made of metal, with polygonal or circular cross section, relatively wider at the base, and tapering with elevation. Such towers typically further comprise structural enhancement attached to the bottom of the monopole, such as base plates. The towers are designed to support specified design loads. However, need may arise after the initial tower installation to exceed specified design loads. Thus it may become necessary to reinforce an existing tower to increase its load carrying capacity, such as to increase capacity to carry combined axial, moment and shear loading.
Antennae impart vertical compressive loads and significant bending moments on the tower. Wind imparts cyclic lateral loads and bending moments, which induces sway causing additional secondary bending moments. Reinforcement means must accommodate these loads.
One existing way to reinforce monopoles is to attach reinforcing rods to the sides of the tower. In such systems, the rods may be embedded in the foundation and tightly attached to the tower using mounting brackets at multiple elevations. An example of a mounting bracket comprises an angle iron bolted to the side of the tower with U-bolts that fasten the rods to the angle iron. Rods spaced a distance outboard of the tower increase the effective cross sectional moment of inertia and bending load capacity relative to the unreinforced tower. To transmit rod loads directly to the ground, some systems embed the rods directly in the tower foundation.
When the entire system is experiencing bending loads, such as under lateral wind loads, individual reinforcing rods on one side of the tower may be in tension while rods on the opposite side may be in compression. Loads in a reinforcing rod may alternate cyclically from tension to compression when the tower experiences back and forth sway in wind.
Existing systems rely on fixed attachment of the reinforcing bar rods at intermediate brackets that are spaced apart at vertical intervals. Fixed intermediate attachment affects the mechanical properties and mechanical behavior of the entire system and individual components thereof, including the pole, the brackets and the rods. The intermediate brackets experience significant loads. In addition, substantial assembly work is involved in making each intermediate connection separately, including mounting each bracket to the pole and mounting each bracket to the reinforcing rod. Typically, existing systems also embed reinforcing rods in the foundation by boring holes in the foundation, inserting rods in the holes, and then filling the remaining space in the holes with adhesive or grout to form the joint between the foundation and rod. This embedding procedure and resulting joint have undesirable qualities, such as undesirable qualities under cyclic loading.
There is a need for a monopole tower reinforcing system with a different type of intermediate support that simplifies assembly, that provides lateral spacing and stability to the reinforcing rods, and that may reduce support loads and provide axial freedom of deflection to the rod. There is also a need for a system that does not rely on embedded reinforcing rods in the foundation and using adhesives or grout to form the joint between the rods and foundation.
The present invention provides a fastener suitable for attaching standoffs and termination brackets to monopole towers in reinforcement systems that fills those and other needs. The fastener has inherent application for fastening parts in general, without need for a threading step to tighten the fastener.